Comparison of cis-trans with E/Z

  Z   ==>  Cis isomer
  E   ==>  Trans isomer

The comparison of E-Z and Cis- Trans is suitable for above type of  isomers only. Not in all isomers. For example.

E/Z notation

E   ==>  Entgegen ( German word ). Two groups of higher priority are on opposite sides of double bond.
Z   ==>  Zusammen ( German word ). Two groups of higher priority are on same sides of double bond.
Example :

       Now we start with the cis isomer, the left end of the double bond has C and H. By the CIP priority rules, C is higher priority than H. ( Due to its higher atomic number ). In cis isomers the right end of the double bond also the same priority. Since the two priority groups are both on the same side of the double bond. Therefore this is (z) 2- butene.
        Now we look at the trans isomer, the higher priority group are on the opposite sides of the double bond. Therefore this is (E) 2- butene.

Example:

Stereoisomerism

                   Isomers which have the same molecular formula and same structure but differ in the arrangement of atoms or groups in space. There are two types of stereoisomerism.

• Geometric isomerism
• Optical isomerism.

Geometric Isomerism:

         Isomers which arise due to the different spatial arrangement of atoms or groups around double bond or in cyclic compounds. In organic chemistry geometric isomerism otherwise known as cis/trans isomerism. Generally such isomers contain double bond , which cannot rorate, and also one form cannot be readily converted into the other form without breakage of a bond. cis and trans isomers occur both organic molecule and inorganic coordination complexes.

Example:

     The identical groups lying on the same side, the diastereomers is referred to as cis. In Latin cis means ' on the same side '

     The identical groups lying on the opposite side, the diastereomers is referred to as trans. In Latin trans means ' across ' or 'on the other side'.

     Disubstituted cyclic compounds can also exist in two different forms.

Example:

Coordination Complexes.

                     In coordination complexes cis isomers in which similar ligands are closer together and trans isomers in which similar ligands are opposite together. Not all coordination compounds have geometric isomers.

Example:

Two isomers of squar planar Pt(NH₃)Cl_2.

Cis isomer used in anti-tumor activity.

Trans isomer does not exhibit any anti-tumor activity.

 

Isomerism

         Compounds having same molecular formula but possessing different properties. This phenomenon is known as isomerism. There are two types of isomerisms.
                        ( i ) Structural isomerism.
                       ( ii ) Stereoisomerism.

Structural isomerism:
         Isomers which have the same molecular formula but differ in their structures. It is otherwise known as constitutional isomerism. It is opposed to stereoisomeris. Different types of structural isomers are given below.

• Position isomerism.
• Chain isomerism.
• Functional isomerism.

Position isomerism:

         In position isomerism a functional group or other substituents changes position on a parent ( main carbon chain ) structure. It is otherwise known as regioisomerism.

Example:

Chain isomerism:

        Chain isomers differ in the structure of their chain ( carbon skeleton ). It is otherwise known as skeletal isomerism.

Example:

But pentane  C₅H₁₂  has three isomers.

Functional isomerism:

           Isomers have the same molecular formula but different functional groups are known as functional isomerism.

Example:  C₃H₆O 

Example: C₂H₆O

 CH₃ – O – CH₃    diethyl ether.

Carbon-oxygen-carbon chain functionality is called Ether.

 CH₃ CH₂ – O – H Ethanol.

Carbon-oxygen-hydrogen functionality is called Alcohol.

Periodic Trends Of Alkali Metals

• Ionization Energy:

Alkali metals have low ionization energy.
                     The first ionization energies of alkali metals are relatively low and decreases on moving down the group.

Reason:
   Atomic radius gets increases on moving down the group. so the outermost electron gets farther away from the nucleus and therefore the first ionization energy decreases.
   The second ionization energy of the alkali metals are high. The second most loosely held electrons is part of a fully filled electron shell and is thus difficult to remove.

• Electropositive Character:

Electropositive character increases go down the group.

                    M      →     M⁺      +     1e^-

Reason:
     The first ionization energy of alkali metals decreases down the group, it is easier to remove the outermost electron from the atom and the participate in chemical reaction thus increasing the electropositivity down the group. The alkali metals are high electropositive that they emit electrons when irradiated with light.This effect is known as photoelectric effect. Due to this property Cs and K are used in photoelectric cells.

• Melting And Boiling Point:

Alkali metals have low melting and boiling point.

Reason:

     The weak interatomic bonds are attributed to their large atomic radii and the presence of one valance electron. The atoms increases in size going down the group. The nuclei of the ions are move further away from the delocalised electrons and hence the metallic bond becomes weaker. Therefore the melting and boiling point decreases going down the group.

• Density:

Alkali metals have high density.

Reason:

     The trends for the densities of the alkali metals depends on their atomic weight and atomic radii. The densities of the alkali metals increases moving down the group with an exception at potassium. Lithium has low density due to the low atomic weight of the atom.

• Oxidation And Reduction:

Oxidation:

     Alkali metals have only one electron in their outermost valence shell. So they easily lose one electron in their outermost shell and form a stable configuration of the nearest inert gas. They are monovalent elements showing an oxidation state of +1.

Reduction:

     Alkali metals have low ionization energy, they easily lose their valence electron. Therefore these elements behaves as good reducing agents

• Atomic And Ionic Radii

            Atomic and Ionic radii of alkali metals are increases on moving down the group. The ionic radii of the alkali metals are much smaller than their atomic radii.

Uses of Hydrogen Peroxide

• Hydrogen peroxide is a bleaching agent delicate materials like silk, wool, hair which wool be destroyed by chlorine, are bleached with hydrogen peroxide.
• It act as a aerating agent in production of sponge rubber.
• It destroys bacteria and hence it is used as an antiseptic and germicide for washing wounds, teeth and ears.
• It is used as a oxidizing agent.
• It is used as an Antichlor.
• It is also used as a propellant in rockets.
• For pollution control of domestic effluents where it restores the aerobic conditions of sewage waste for pollution control of industrial effluents containing CN^-  ions. H₂O₂  oxidizes CN^- ions to harmless product. 

Chemical Properties Of Hydrogen Peroxide

Decomposition:
           Pure hydrogen peroxide is unstable and decomposes on standing. On heating water and oxygen are formed.

                             2H₂O₂     →     2H₂O     +     O₂ 

_{Oxidizing Nature} 

        It is a powerful oxidizing agent. It functions as an electron acceptor.

                              H₂O₂     +     2H⁺     +     2e^-     →     2H₂O

                                                                                  (In acidic solution)

                                               H₂O₂^-     +     2e^-     →     2OH^-

                                                                                   (In alkaline solution)

                                              2KI     +     H₂O₂      →     2KOH     +     I₂

                                                                                     (In neutral medium)

It oxidizes ferrous salts into ferric salts.

                           2Fe²⁺     +     2H⁺     +     H₂O₂     →     2Fe³⁺     +     2H₂O

Reducing Agent :

                        Ag₂O     +     H₂O₂     →     2Ag     +     H₂O     +     O₂

              Hydrogen peroxide act as a reducing agent. In above equation moist silver oxide is reduced to silver.

Addition Reaction: